Midface Distraction Advancement in the Canine Without Osteotomies

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Abstract
Midface hypoplasia, often associated with exorbitism and malocclusion, has been traditionally corrected by using Le Fort advancement osteotomies through wide surgical exposure. These procedures suffer the disadvantages of hemorrhage, unpredictable bone graft resorption, the need for retained hardware, and bone graft donor-site morbidity. We present an investigation of midface distraction in the canine without osteotomies. Five canines were the subjects of this study and were divided into two groups. At the time of placement of the lengthening devices, Group 1 animals were 10 weeks of age and Group 2 animals were 5 years of age. Under general anesthesia, four modified Hoffman bone distractors were mounted on 2-mm half pins placed individually across the nasofrontal and the zygomaticotemporal sutures on each side of the craniofacial skeleton. Distraction of all devices was begun on postoperative day 1 at the rate of 0.5 mm/day for 4 days and then 1.0 mm/day for 28 days, after which interval the devices were removed. The dogs were serially monitored and examined for 3 months. One dog in the first group served as a sham control. The results were assessed by standardized cephalograms, and craniofacial computed tomographic scans with three-dimensional reconstruction performed before device placement as well as after removal of the device. In one Group 1 animal, computed tomographic scanning was performed every 2 to 4 weeks for 3 months. Gross examination of the Group 1 animals demonstrated the development of enophthalmos, dolichocephaly, and a class II malocclusion-overbite. No evidence of distraction or advancement of the midface was observed in the Group 2 dogs. Midface distraction is feasible in the immature animal. If miniaturized devices could be developed, the clinical implications for young patients with midface hypoplasia may be significant.

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